arjunchopra

I have seen threads , " Whereby excess Epoxy is being removed

with the help of Plastic cards ie like Credit / ATM Cards / Thick

Plastic Strips .

How woudl u remove the excess Wpoxy qwithout disturbingthe FS Cloth , as the cloth would move and mess the entire Glassing process.

Need ur inputs on this ?

Cheers.

Arjun

Ed Smith

Here is how it is done. Lay the DRY cloth over the surface. Brush or pour some resin on to the surface. Carefuly spread the resin over the whole surface, either by brush or scraper. Starting at one end scrape the resin off. The cloth will stay stuck to the wood. There may be some wrinkling but these can easily be smoothed out. Excess resin is returned to the cup.

Ed S

arjunchopra

Ed ,

When u start scraping the excess epoxy, wont the epoxy & the glass mix which by then becoems gueey get removed with the excess.

When u say resin , do u mean resin with the hardener, or jsut plain resin .

Woudl liek to have ur feedback .

Cheers.

Arjun

Steve Lewin

It sounds like you may be thinking of CSM (chopped strand mat) glass. The plastic card method only works successfully with woven glass cloth which is what is used for skinning wings etc. You can't possibly remove parts of the "glass mix", the glass cloth is all in one piece.

In my limited experience CSM is only used for making fairly large mouldings. In this case you do not want the remove the resin.

Steve

KevinSheen

I remove excess resin with either a toilet paper roll or paper towel roll but you are right, you have to be careful not to move the fiberglass.

In bagged wing layups, I've had luck drying the roller with a glob of paper towels and then re-rolling the cloth.

Kevin

Ed Smith

I will not describe vacuum bagging as that is not the queston you asked.

I would not recommend the toilet paper or paper towel method of soaking up resin as you then have a pile of sticky paper towels to get rid of.

When I say "Resin" I mean the completely mixed resin and hardener. With the squeegee method there is nothing to get rid of. The scraper can be wiped clean and used again. When doing a wing do one surface first. When cured sand off the edge overlap and then do the other surface. Pay particular attention to the leading and trailing edges. Ensure that the cloth is well saturated along those edges.

If you intend to glass a fuselage with compound curves it is not very easy to squeegee without getting ridges caused by the scraper. Maybe the paper towel method has some merit there. I prefer to be extra careful when doing fuselages. I warm the resin and brush on lightly. The warm resin will go on much smoother and thinner. However, if warming up the resin use a slow hardener.

Ed S

probligo

Arjunchopra,

This is one of those techniques that is easy- too easy to mention - but almost impossible to describe.

Most of the story is in this thread already, but as a summary...

Cut glass cloth to size.

If you are not sure about this, miss these next two steps and lay the glass dry onto the area you are covering...

Spread a thin coat of matrix (that is your resin/hardener mix) over the area that you are covering.

Lay the glass cloth carefully over the area, making sure that you get out any wrinkles as you go.

(Note that if you are laying more than one layer of glass/cf/etc then this is a technique well worth learning - of being able to put dry cloth into the matrix and work it in...)

Pour/brush matrix onto the cloth evenly across the area. Brush is best...

Use your expired credit card to smooth the glass cloth and press the matrix into the cloth.

Work from the centre out towards the edges, not like a brush.

Press firmly but only sufficient pressure to work the matrix along the cloth.

You will know that you have got it right when the glass is completely wetted with matrix but you can see the weave of the cloth.

Do not pull the card/wiper off the cloth, "wipe it off"

Do not expect to recover all of the excess matrix.


I would not recommend using paper towels and such to mop the excess matrix. By the time you get to this point the matrix will be starting to go off on the surface, and you run the strong risk of lifting the glass cloth away from the surface underneath. Wipe the excess into the spare cloth around the margins and clear of your surface.

If you want to go this extra step (and I for one dont think it necessary if the weave is standing out of the matrix) then use a rip cloth to protect the glass and matrix. But as someone else has said, by this point you are getting into the vacc-bag techniques.

arjunchopra

Probligo ,

Need clarification on the following points mentioend by u :

1 - Do u need to apply a layer of epoxy on the wing surface & then lay up the clon top of it . Then again add Epoxy on the cloth so it is completely saturated .Won't this make it a bit heavy .

2 - Do u use normal Z- Epoxy or finishing resin . What is the difference .

3 - How do u sand it . I tried sanding mine , Very difficult . Quite hard when set . I have used Alcohol & Epoxy mix.

Cheers.

Arjun

probligo

Arjun,

This is where a bit of practice comes into play.

I have used this technique a lot on wings for freeflight towline gliders and FFHLGs. Because these are based around balsa open frame and 1mm sheet D-boxes they can not be vacc-bagged, and this is about the only way of doing it.

First, you gotta learn to work fairly quickly. A 3 hour epoxy will start going off in about 15 minutes if the temperature is over 23C. You might need to look at getting a retardant with your epoxy, or crank the ol' air conditioning up a bit

To answer your questions.

1. Yes. But do not wait for it to dry. The whole secret here is that you are working on the liquid epoxy.

2. I use a marine (boat-building) epoxy that I find has good stiffness, good resistance to abrasion, works easily etc etc. I dont know what you have available on your markets but what you want is an epoxy that is about mid-range or just below in flexibility. Shop around, ask questions and tell people what you want the epoxy for so that they can get an idea of what will be required. A lot of the guys hereabouts use a West Systems epoxy and rate it very highly. I have never tried it (too conservative )

3. If you can get to doing this right you should not sand it because there will be so little resin left that you will be sanding the glass cloth/cf whatever and breaking the strands that make the strength. For this reason, your surface has to look like the finished item before you put the matrix on it.

OK? To repeat:

Apply thin coat of matrix to surface. One thing I am trying on my current build is to seal the balsa surface with dope before applying the glass/cf spars that I am using.

While the matrix is still wet lay cloth and rub down with credit card

Matrix should start coming up through the weave.

If you are applying more than one layer of glass, put the next layer on now and repeat...If the glass does not have matrix coming through the weave then it is not properly wetted out and you need to drop more matrix on those spots.

Apply more matrix over the top, spread out with credit card. This is where practice again becomes important. I get off all the matrix until I can hear the credit card rubbing over the cloth. (Kinda like a faint buzzing noise and the matrix coming out of the cloth will look bubbly like cocacola). Take any more out and the glass will separate from the panel again or bubble. If you want a totally smooth surface then you want to back off from that just a little.

That is judgement and practice.

Good luck...

boater

My Feedback: (2)

The soak-up-the-resin method came from the old K&B Polyester resin days. I used to fly Formula 1 many years ago. The method went like this: Get your wing all prepped. Lay out 3/4 oz cloth over one side of the wing and cut 1" oversize. Mix up a couple oz. of resin and hardener. Brush on your resin starting at the center and working to the edges. Take a roll of toilet paper and roll the surface of the cloth/resin so that the paper don't unwind. This will remove the excess resin. Pull off the outer layer of paper and do it again till you're happy. The glass and balsa should end up with a light coat of polyester and no shiny spots. A dry application like this is to apply just enough resin to attach the glass, but not let the balsa keep soaking up resin and weight, also you don't want the glass floating away from the balsa on excess resin. When hardened, use sandpaper on the edges to break off the glass and do the other side. After both sides are done, sand the entire wing lightly to remove high spots only and fuzz. Another light coat of resin over the the first to fill the weave. Sand the second coat to prep for primer. I don't think this applies to mold lay-up, cause soaking up to much resin will lead to too many pin-holes.